A cathode-ray tube (CRT) is a vacuum tube of a particular structure, which is useful to various electronic apparatus called a general display such as a television receiver, an oscilloscope, and a computer monitor. The original function of the CRT is to convert information included in an electric input signal into optical beam energy, which is then visibly displays the electric input signal.
In the CRT, the electrons emitted from the thermionic cathode are controlled by a control grid. The electronic beam through anode accelerates by magnetism or static electricity and deflects from a magnetic deflection coil or an electrostatic deflection coil on axes of the vertical or horizontal direction. Then, the electronic beam impacts upon a fluorescent film and is emitted as a visible ray for a while.
The input signal having information to be displayed is provided to a plurality of grids and cathodes. However, since beam current called gamma characteristic is a nonlinear function of control voltage, the more complicated compensating circuit should be disposed between the input signal and the plurality of grids to provide linear display intensity.
During the last several years, the trend is moving from a plate display towards development of a non-thermionic cathode, i.e., a field emission array.
The use of the field emission cathode array, instead of the conventional thermionic cathode in the CRT provides some merits. In particular, the use of the field emission cathode enables current density to be very high and lengthens the life of the CRT by eliminating a heat element.
However, according to the field emission cathode, the emission amount of electron for the input signal can be more non-linearly changed than in the thermionic cathode, so that there should be the a more complicated compensating circuit in the field emission cathode.
In order to solve such a problem, here are two cell driving devices of the FED, one of which is based on a passive matrix addressing method disclosed in U.S. Pat. No. 5,103,145 and proposed by Doran. The other is based on an active matrix addressing method disclosed in U.S. Pat. No. 5,210,472 and proposed by Casper.
According to the U.S. Pat. No. 5,103,145, the cell driving device of the FED in accordance with the passive matrix addressing method converts an input signal into a digital signal and linearly increases the emission amount of the electron by increasing the number of cathodes driven depending upon a logic value of the digital signal. In this case, more gray levels are implemented by the number of cathodes. Thus, it is difficult to embody the gray levels over a predetermined limitation because the number of cathodes to be installed in an occupying area of the cell could be limited.
In addition, the cell driving device of the FED in accordance with the passive matrix addressing method employs a voltage driving method which permits the electron to be emitted by voltage differential between the cathode and a gate. However, in this case, the current for voltage is changed non-linearly. Therefore, there may arise a problem may arise because it is hard to accurately regulate the amount of electrons emitted from the cathode.
On the other hand, the cell driving device of the FED according to the active matrix addressing method disclosed in the U.S. Pat. No. 210,472 is intended to drive pixels of high electric field under use of an integrated circuit consisting of CMOS or NMOS transistors and an input signal at a low voltage. Also, the cell driving device of the FED according to the active matrix addressing method uses a MOS transistor at a high voltage as a scan and a data switch in order to drive the cathode arranged in row lines and column lines. Further, the cell driving device of the FED according to the active matrix addressing method comprises fuses connected between a column driver and the cathode, a field effect transistor coupled between the cathode and the gate. The fuses limits the current so that overcurrent is not applied to the cathode. The field effect transistor used as a resistance regulates the amount of the electron emitted from the cathode by regulating the voltage differential between the cathode and the gate terminal through the adjustment of its own resistance value. Thereby, the light degree of the screen is adjusted. The column driver implements more gray levels by regulating the time required in driving the cathodes of the column lines, i.e., duty cycle.
However, the cell driving device of the FED according to the active matrix addressing method should use the MOS transistor for high voltage in order to switch a high-voltage supplied to scan and data lines. Further, the cell driving device of the FED according to the active matrix addressing method should be subjected to form a thick gate terminal of the field effect transistor coupled between the gate terminal and the cathode. Thereby, the cell driving device of the FED according to the active matrix addressing method needs more transistors than that of the FED according to the passive matrix addressing method and its manufacturing process is complicated.
Moreover, the number of adjustable duty cycles for implementing the more gray levels is limited, so that it is impossible to embody the gray levels over a predetermined limitation.